This invention relates to hydraulic fluid pressure energy translating machines or devices. In particular, this invention relates to hydrostatic barrel support bearings for parallel disposed multi-piston machines of the type used to convey or respond to hydraulic fluids, or the like.
Conventionally, such machines comprise a rotatable cylinder block or barrel containing a plurality of parallel axially-extending pistons disposed equi-angularly about the central axis of the block. A cam plate is provided at one end of the barrel for engaging bearing shoes provided on each of the pistons and for respectively reciprocating each piston or rotating in response to the pistons as fluid moves into and out of each piston-containing cylinder. Such machines are generally equipped with ported head means for providing a valving action for ingress and egress of fluid into and out of the cylinders of the machine. The port means further typically is formed in means such as a cap at the head end of the housing that also has means that provides a hydrostatic bearing area against which the axial thrust of the barrel may be balanced. This bearing is generally provided by flowing oil across sills at the interface of the head and barrel surrounding the ports which minimizes contact of these elements and prevents seizure.
Although it is highly desirable from the standpoint of control of fluid leakage and the maintenance of adequate lubrication to have the head and barrel mating surface properly spaced and aligned, this alignment is usually difficult to maintain during operation of the machine due to the well-known propensity of the barrel to tilt in a radial direction. This effect is primarily caused by radial components of force acting on the barrel through the pistons being in different planes. When the barrel tilts as a result of these forces, the mating surface of the barrel and bearing surface of the head are urged out of alignment into an inclined position, resulting in undesirable fluid leakage, and disruption of the lubricating oil film.
The problem of barrel tilt is especially severe with inset porting, i.e., where the cylinder ports are inset toward the barrel axis side of the cylinders. This inset of the ports is found to improve cylinder filling and is especially desirable for high-speed pumps and motors.
Additionally, in conventional axial piston-type fluid machines, the barrel has a tendency to move axially against the bearing surface of the head during operation of the machine in response to axial components of force generated by the pressurized fluid in the cylinders. This net force urging the barrel against the head, generally termed the hydraulic clamp force, tends to reduce clearance between the bearing surface of the head and the barrel mating surface, and acts in opposition to the hydrostatic bearing provided at this interface thereby decreasing the clearance between the barrel and head. In the event, for example, of transient over pressure in the cylinders, the hydraulic clamp force may significantly increase, and the concomitant decrease in bearing clearance at this interface results in wear and galling on these elements, and occasional seizure. As the rotational speeds increase, the forces tending to cause axial and radial displacement of the barrel also increase, disrupting the alignment and the clearance between the bearing surface of the head and the mating surface of the barrel, or "bearing clearance," thereby resulting in fluid leakage and/or insufficient lubrication of the head/barrel interface.
Inset porting also tends to cause an imbalance of moments on the barrel further aggravating these problems. This is caused by the centroid of the clamping forces not being colinear with the centroid of the separating forces. This results in higher tipping moments due to non-colinearity of clamping and separating forces.
These problems have been recognized in the prior art, and numerous solutions proposed therefor, such as those described in U.S. Pat. Nos. 3,183,846; 2,735,407; 3,267,871 and 3,292,553, including means for laterally stabilizing the cylinder barrel such as described in U.S. Pat. No. 3,267,871 and floating valve means such as described in U.S. Pat. No. 2,649,741. Other approaches are shown in 2,298,850; 3,267,871; 3,702,576, and 3,747,476. However, none of these known prior art solutions have proved entirely satisfactory. For example, difficulties have been encountered in resolving the attendant problems of maintaining satisfactory head/barrel clearance under variable operating conditions in pumps having axially floating barrels, wherein substantial variations in temperature, pressure, rotational speed, vibrations and other factors occur. It is highly desirable that means be provided for simply and effectively compensating for the variable forces developed within the pump to maintain adequate head clearance during pump operation, for controlling fluid leakage which impairs the efficiency of the pump, and for accommodating an adequate lubricating oil film between the head/barrel interface which prevents excessive wear, or in extreme cases, seizure of these elements.